Twelve nephrectomies (NEs) were performed in 12 pigs (11-17 kg). Total NE was performed on the left side and partial NE on the right side (lower third of the kidney), thus two-thirds of the total kidney volume was removed. Renal function was studied with 99mTc-diethylenetriaminepentaacetic acid (DTPA) renography and serum urea and creatinine levels preoperatively, and 1 and 2 weeks postoperatively. The pigs were imaged in each session for 30 min by collecting 10-s frames from a posteroanterior (PA) view of an anaesthesized animal. The injected activity was 37 MBq. Serial blood samples were taken from the subclavian vein at 0, 1, 2, 3, 5, 15, 25, 40, 60 and 120 min (six animals) after 99mTc-DTPA injection. The DTPA disappearance rate (DDR) was determined from these samples and in other cases (six animals) a blood sample at 20 min was used. The DDR was also determined from the dynamic gamma imaging data: Regions of interest (ROI) were upper body, spleen, heart and kidneys. The ROI analysis correlated well with the blood sampling data (r = 0.97, P < 0.0001). The reference values for pig DDRs were 0.99 +/- 0.08%/min. These values were 0.71 +/- 0.08%/min at 1 week postoperatively and 0.63 +/- 0.08%/min at 2 weeks. DTPA clearance rates were preoperatively 0.53 +/- 0.06 ml/s; at 1 week postoperatively 0.41 +/- 0.06 ml/s; and at 2 weeks 0.35 +/- 0.06 ml/s. There were no significant differences pre- and postoperatively in creatinine and urea concentrations. The DTPA clearance (ml/s) and disappearance rates (%/min) when determined per kidney area (cm2) increased significantly (P < 0.001 at both 1 and 2 weeks); in 11 of 12 animals the function of the resected right kidney was higher than the split function of the whole right kidney preoperatively. Unilateral nephrectomy initiates a functional adaptation or a growth response in the contralateral kidney to compensate for the loss of a renal mass. These data also indicate that two-thirds of the kidney volume in young pigs can be removed without danger.